Clinical otosclerosis has a reported prevalence of 0.2 - 1% among white adults, making it the single most common cause of hearing impairment in this population. Mean age-of-onset is in the third decade, and 90% of affected persons are under 50 years of age at the time of diagnosis. It is characterized by isolated sclerosis of endochondral bone of the inner ear. Conductive hearing loss develops when otosclerotic foci invade the stapedio-vestibular joint (oval window) and interfere with free motion of the stapes. Sensorineural hearing loss may also be present. Although the sensorineural loss cannot be corrected, stapes microsurgery has proven to be a successful means to restore normal ossicular conduction and can improve hearing thresholds. Families with autosomal dominantly inherited otosclerosis have been described, but in most patients the etiology of the disease is unknown.